I’m starting to build a modular synth for the first time and am pretty proud of how I have done so far (cutting a few corners at the cost of aesthetics!). I’ve built 13 of the Super Simple Oscillator circuits and would like to build a pitch shifting module to be able to control the relative pitch/tuning of all the drones at the same time. I’m not sure if anyone has done a stripboard layout for this sort of thing before, but I am unable to find it if there is Any help would be greatly appreciated (I’m not wanting to conform to volt per octave standards just yet!)
Thanks,
Alfie
P.S. I’m sticking to stripboard layouts at the moment as I am struggling to read proper circuit schematics, if anyone knows of any resources etc that might help me to learn how to interpret these, I would be very much appreciative.
Oh amazing, thank you so much for this, I didn’t know that simply increasing the resistance along the positive power line to the modules would change the pitch in this way.
Just a similarly related note to this, if I’m trying to change the volume of the output using a passive attenuator (basically running the signal through a potentiometer), and finding that it is also changing the pitch, would I be able to use a diode to stop the pitch from changing?
The ground/sleeve of the jacks are connected together, tip of input Jack goes to right hand leg of pot, middle pot leg to tip of output Jack and left hand leg is connected to ground.
What is the output connected to? Sound card, amplifier, powered speaker?
Whatever it is, if it had infinite resistance to ground then changing the pot can change neither the current flowing out of the oscillator nor the voltage at the oscillator output. So the oscillator would not be affected.
Since it is, that implies the downstream resistance to ground is small enough to affect the oscillator. When you change the pot you change the load resistance.
In your oscillator is the output resistor connected between the pitch pot and the transistor emitter, or between the LED and the transistor collector? Last time I built one of these the former was about 400 mV peak to peak on a 7 V offset while the latter was 100 mV on a 700 mV offset. In the former case you’re well above the diode forward voltage and the diode has only a small effect on current and voltage. In the latter case you’re near or below the forward voltage, very little current gets through the diode, and the output voltage is close to zero. Either way I wouldn’t expect a diode to fix the problem you mention.
The usual way to isolate a signal from the effects of a variable load resistance is to buffer it with an op amp.
Added: Oh, what’s the value of the output attenuator? The smaller it is the less the downstream device will affect it. However, the smaller it is, the smaller the output voltage will be since it makes a divider with the oscillator’s 100k.
(Presumably the “1m” resistor is really 1M.) I’m not sure what D30 is for.
I built this on a breadboard (without the MOSFET or the diode) and connected it to a powered speaker. I couldn’t hear any output at all until I changed R22 to 100k and then indeed the pitch changed as I changed RV21. I tried moving RV21 from the collector to the emitter. As expected from my previous build the output was much lower, barely audible at all in fact, but it also changed pitch when I changed RV21.
Moving back to the collector I tried adding a diode after R22. It didn’t change the behavior appreciably.
All my pots in the passive attenuators are 100k, and I have since rectified the problem (I think) by adding a TL072 circuit like you suggested above. Again, as my experience as well as knowledge is fairly lacking still (I prefer learning as I go along), I have run into another problem regarding the output of this set of oscillators.
Originally, I merged all the signals by joining all the ground wires of the output jack sockets, and then doing the same with the tips of the jacks, only with a 470r resistor on each to avoid clipping/distortion I presume? Anyway, I have since merged them into a TL072 circuit (here: LMNC Super Simple Mixer [Strip Board Layout + BOM]), expanding on this example, from 3 inputs all the way up to 10. Also, as I want all the inputs to be at the same volume level, I skipped out on the paotentiometers and wired the pink output lines in the diagram straight from the input jacks into the stripboard circuit.
Now those are the only changes I have made to the schematic, and it works fine, the pot I inserted before the output jack lowers the signal level without changing the pitch at all, that is perfect. The issue arises when I send signals to more than 2 of the input jacks. The moment a third is connected, all the signal cuts out completely and I have no idea why, Sam in the Super Simple Mixer post. says that in theory, I should be able to connect as many inputs as I want, so unless I have gone wrong somewhere, I don’t see that it would be an issue with the circuit? I wonder whether it may be an issue with the TL072 chip itself but it merges the first two signals with ease and so I’m finding myself fairly stuck at the moment.
As always, I really appreciate all the help or advice I can get and once again, thank you very much for all your help!
If the inputs are coming directly from the oscillator emitters they probably have a several volt offset. Add several together and you get a >10 V offset which saturates the op amp. You could try a capacitor before each input resistor for AC coupling. About 1 to 10 uF.
Yes, and no. You won’t easily find ceramic caps in that range. 1 uF film caps would be a possibility, higher value would almost have to be electrolytic. + side toward the oscillator.
Any help would be greatly appreciated (I’m not wanting to conform to volt per octave standards just yet!)
